1. Field of Invention
The present invention relates to a damping force control valve and a shock absorber using the same, and more particularly, to a damping force control valve having an orifice installed to an inlet of a pilot channel to give a high-speed damping force when a shock absorber is operated in a soft mode, and a shock absorber using the same.
2. Description of the Prior Art
Generally, a shock absorber of a vehicle is installed to a moving means such as a car, and thus, absorbs or buffers vibrations or shocks transferred from road wheels in contact with a road surface.
This shock absorber can improve the ride comfort by lowering a damping force and thus absorbing vibrations caused by unevenness of a road surface when a vehicle is ordinarily running, and enhance the handling stability by raising a damping force and thus restraining posture change of the vehicle body when the vehicle turns, accelerates, brakes or runs at high speed.
Meanwhile, in order to improve the ride comfort and handling stability, a shock absorber is recently provided with a damping force control valve mounted to one side thereof so as to suitably adjust a damping force, so that it is developed up to a damping force control shock absorber capable of suitably controlling a damping force according to a road surface state a the running state.
In general, most of conventional damping force control shock absorbers control a damping force in an actuator manner, and are mainly classified into a reverse type and a normal type depending on a damping force control method.
The aforementioned damping force control shock absorber is configured to increase or decrease both rebound and compressing damping forces at the same time according to an actuator current. For example, the conventional damping force control shock absorber controls a damping force in rebound and compression strokes in a soft mode by application of a certain actuator current, and also controls the damping force in a hard mode by application of a higher actuator current. Such damping force control is realized in such a manner that a spool moving according to the actuator operation controls back pressure formation in and adjustment of a pilot chamber formed in the rear of the damping force control valve.
FIG. 1 is a sectional view showing a conventional damping force control valve of a shock absorber.
A conventional damping force control valve 10 includes a spool rod 20 installed to an upper portion of an actuator 15 and having a plurality of channels allowing fluid communication, and a spool 25 installed to the spool rod 20 and operated by the actuator 15 to open and close each channel, as shown in FIG. 1.
In addition, a first ring disk 32 acting as a fixed orifice is installed to the spool rod 20, and a lower retainer 34 having a communication port 34a allowing fluid flow is installed to an upper portion of the first ring disk 32.
Also, a second ring disk 36 acting as a main valve is installed to an upper portion of the lower retainer 34. The second ring disk 36 partitions a pilot chamber 45 formed in the upper portion of the lower retainer 34 from a high pressure region Ph. In addition, an upper retainer 38 having a communication port 38a allowing fluid flow is installed over the lower retainer 34.
Then, a nut 27 is coupled to the spool rod 20 to join the lower retainer 34 and the upper retainer 38. Meanwhile, a spring 23 is interposed between one end of the spool rod 20 and the spool 25, so that the spool 25 is brought into close contact with to the actuator 15.
The spool 25 has a hollow portion (not shown) and a plurality of vertically stepped outer diameters. Here, an upper spool slit 25a and a lower spool slit 25b are defined by the stepped outer diameters of the spool 25. At this time, the upper spool slit 25a is formed to be larger than the lower spool slit 25b, so that when the spool 25 reciprocates, the area change of the upper spool slit 25a with respect to the communication ports 21a, 21b and 21c of the spool rod 20 is greater than that of the lower spool slit 25b with respect to the communication port 34a of the spool rod 20.
Referring to FIG. 2, which is a schematic hydraulic circuit diagram showing a channel in the conventional damping force control valve, the operation of the conventional damping force control valve 10 so configured will be explained.
As mentioned above, the damping force control valve 10 includes a first channel Qm having a main valve Km, a second channel Qr having a first variable orifice Kr, and a third channel Qc having a second variable orifice Kv and a fixed orifice Kc.
In the damping force control valve 10, the movement of the spool 25 controls the flow of the fluid that moves from a high pressure region Ph to a low pressure region Pl. When the spool 25 moves as mentioned above, open areas of the first variable orifice Kr and the second variable orifice Kv are varied.
At this time, the first variable orifice Kr has an area change ratio greater than that of the second variable orifice Kv, and allows fluid to flow from the high pressure region Ph to the low pressure region Pl. Here, the area of the first variable orifice Kr is decreased as that of the second variable orifice Kv is increased, while the area of the first variable orifice Kr is increased as that of the second orifice Kv is decreased.
The first channel Qm determines a valve characteristic in a middle high speed range of the soft/hard mode and has a spring preload in the form of a relief valve. Also, the pilot chamber 45 is formed in a rear surface of the valve and thus its pressure determines a valve opening pressure, thereby making the damping force control possible.
In addition, the main valve Km is opened at different pressures according to a pressure Pc of the pilot chamber 45. The pressure Pc of the pilot chamber 45 is formed by the operation of the second variable orifice Kv installed in an upstream of the third channel Qc and the fixed orifice Kc installed in a downstream. Thus, the pressure of the pilot chamber 45 increases by controlling the area of the second variable orifice Kv, whereby the damping force characteristic is converted into the hard mode.
At this time, the sectional area of the second variable orifice Kv is decreased as that of the first variable orifice Kr is increased, while the sectional area of the second variable orifice Kv is increased as that of the first variable orifice Kr is decreased.
In addition, the second channel Qr determines a low-speed damping force characteristic in the soft mode, and its area is changed by the first variable orifice Kr to determine a damping force.
Also, the third channel Qc is configured such that the second variable orifice Kv is installed to its inlet and the fixed orifice Kc is installed to its exit so as to form a pressure of the pilot chamber 45.
In a case where the damping force characteristic formed in such a structure is the soft mode, if a predetermined current is applied to the actuator 15, the area of the first variable orifice Kr is increased to lower a low-speed damping force, and at the same time, the channel of the second variable orifice Kv is closed to lower the pressure of the pilot chamber 45, so that the main valve Km is opened at a low pressure.
In the meantime, in a case where the damping force characteristic is the hard mode, if a high current is applied to the actuator 15, the spool moves upward to close the first variable orifice Kr and open the second variable orifice Kv, thereby increasing the opening pressure of the main valve Km and thus increasing a damping force.
Meanwhile, in the conventional damping force control valve 10 and the shock absorber using the same, when an electric or mechanical trouble causes a system malfunction to occur and thus a current is not input to the damping force control valve 10, the damping force characteristic is fixed to the soft mode. If a steering wheel is excessively turned when the damping force control shock absorber is operated in the soft mode, the vehicle can overturn. In order to solve this problem, it is suggested in U.S. Pat. No. 6,000,508 (Dec. 4, 1999) that a restoring means such as a spring is installed to a general pilot control damping valve and a spool moves by the elasticity of the spring so that a shock absorber can be operated in a middle mode having a damping force in a middle level.
However, in the conventional damping force control valve and the shock absorber using the same, the installation of the restoring means for restoring the spool causes the product size to be increased. In addition, the restoring force of the restoring means is operated even in a normal operation, thereby disturbing rapid control of the damping force. Thus, there is a need for developing a shock absorber capable of controlling a damping force in a middle mode without installing any additional restoring means to the shock absorber.